1068
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of the HUMAN
FACTORS
AND ERGONOMKS
SOCIETY
42nd ANNUAL
MEETING-1998
Intended Carefulness For Voiced Warning Signal Words
Rana S. Barzegar and Michael S. Wogalter
Department of Psychology
North Carolina State University
Raleigh, NC 276957801
ABSTRACT
Design standardsfor print warnings (e.g., signs and labels) recommendthe use of signal words to convey
the presenceand level of a hazard. However, very little researchhas been conducted on the use of signal
words presented auditorily. In the present study, 43 voiced signal words were examined as a function of
several factors: voice style (monotone, emotional, whisper), sound level (low, high), participant group
(college students,community volunteers) and gender of the speakerand the participant. Results indicated
that auditory presentation yielded a pattern of connoted hazard levels (ratings of intended carefulness)
similar to previous research using visual presentation. Emotional voicing produced significantly higher
carefulnessratings than monotone or whisper voicing (with overall sound level held constant). Female
speakersproduced significantly higher carefulnessratings than male speakers. Implications for the design
of speechwarnings are discussed.
INTRODUCTION
Signal words in warnings are intended to convey the
presence and level of a hazard. The American National
Standards Institute (ANSI, 1991, 1998) recommends the
terms DANGER, WARNING, and CAUTION to represent
high to low hazard levels, respectively (e.g., ANSI, 1991,
1998; FMC Corporation, 1985). According to ANSI (1991,
1998) DANGER is to representimmediate hazardswhich will
result in severe personal injury or death. WARNING is to
represent hazards or unsafe practices which could result in
severe personal injury or death. CAUTION is to represent
hazards or unsafe practices which could result in minor
personal injury and/or property damage. Interestingly,
researchhas consistently shown that people generally do not
perceive much difference between WARNING and
CAUTION (e.g., Wogalter & Silver, 1990, 1995).
In addition to the standard three signal words, ANSI
(1991, 1998) suggests the term NOTICE be used to
communicate important, but non-hazard related information.
Research has also examined other potential signal words
(Wogalter & Silver, 1990, 1995). The term DEADLY has
been examined in a number of studies. This research shows
that it connotes a higher level of hazard than the term
DANGER (Wogalter & Silver, 1990, 1995; Wogalter,
Frederick, Herrera, & Magumo, 1997).
The signal word standardsand most researchon the topic
have primarily concerned their use in the visual medium, such
as on printed warning signs and labels. Until recently,
virtually no researchhas investigated their use in the auditory
medium such as in voiced or speech warnings. Technology
has now made available digital voice chips that allow the use
of voiced warnings in situations heretofore not considered
possible or practical. Their use may offer advantagesover
print warnings in certain circumstances. One relates to the
People’s attention does
characteristic of omniditionality.
not need to be visually directed to a particular location to
receive the message. Researchalso suggeststhat individuals
are more likely to comply with a warning presentedby voice
than the samemessagepresentedby a printed sign (Wogalter
dz Young, 1991; Wogalter, Racicot, Kalsher, & Simpson,
1994).
In comparison to simple nonverbal sounds (e.g., buzzers
or beeps), speech warnings take advantage of people’s
existing knowledge. A voice yelling “Fire” has more
meaning than a simple bell or siren. Researchon non-verbal
auditory signals has noted that various sound parameters(e.g.,
loudness,rate, pitch) affect perceived urgency (e.g., Edworthy
& Adams, 1996). The concept of perceived urgency has been
used mainly in the auditory warning domain but it is similar
to other measuresused to evaluate visually-presented signal
words, e.g., arousal strength and perceived hazard
(e.g.,Wogalter & Silver, 1990, 1995). In research on print
warnings, perceived hazard has been shown to be related to
other warning-related measures such as nonfamiliarity and
complexity of products, injury severity, intentions to be
careful, and compliance (Laughery, Wogalter, & Young,
1994).
Recently, research has begun to investigate the effects of
auditorily-presented signal words (Barzegar & Wogalter,
1998; Edworthy, Clift-Matthews, & Crowther, 1998). Two
main issues have been of interest. One is whether signal /
/
PROCEEDINGS
of the HUMAN
FACTORS
AND ERGONOMICS
words presentedauditorily have the same effects as shown in
previous researchpresenting them visually. The other issue is
whether it matters how the terms are voiced. For example,
Mershon and Philbeck (1991) found results that suggested
that a whisper sound produces a greater startle reaction than
conversational speech. Edworthy et al. (1998) found that the
style of speech (appropriate vs. inappropriate) affects
perceived urgency. Barzegar and Wogalter (1998) reported
that signal words voiced in an emotional tone received higher
‘intended carefulness’ ratings than words spoken in
monotone. In addition, signal words spoken by female
speakersreceived higher ratings than those spoken by male
speakers.
The present study is an extension of the initial Barzegar
& Wogalter (1998) report. In that report, only data from
college studentswas described and the analysis was limited to
a small subset of five signal words from a list of 43. In the
present study, we include a broader sampleof participants in
addition to the college studentsto determine whether the same
or different results would be found. In this report we present
statistics for the full set of (43) signal words.
The present research examined the following factors:
population group (students, community volunteers), sound
level (low, high), speaker gendg participant gender, voice
style (monotone, emotional, whisper), and 43 signal words.
In general, we expected1 louder words would produce higher
ratings than less loud words. The manipulation of monotone,
emotional, and whisper voicing was included to investigate
whether the characteristics of the voice presentation make a
difference. Another issue is whether the gender of the
speaker influences perceptions of participants. Social
psychology research (e.g., Baron & Byrne, 1997) suggests
that people’s interactions with others can be affected by the
gender of the individuals involved. For this reason we also
included both speakerand participant genderas factors. A list
of 43 signal words compiled by Wbgalter and Silver (1995)
was usedas stimuli.
METHOD
Participants
A total of 144 individuals participated. Seventy-two were
undergraduate students at North Carolina State University
who received researchcredit in their introductory psychology
courses. They had a mean age of 19 years. The other 72
participants were volunteers from the surrounding Raleigh,
North Carolina community (mean age of 34 years, SD = 9.0).
The educational levels attained by the community volunteers
were: 7% completed high school, 21% completed some
college or trade school, 44% completed college, 18%
completed a Master’s degree, and 8% completed a PhD
degree. Ninety percent of the community VOhnteerS Were
Caucasian,7% were African American, and 3% listed other
race/ethnic categories. All community volunteers reported
that English was their first language. Fourteen percent
SOCIETY
42nd ANNUAL
MEETING-1998
believed they had somehearing difficulty; however, only one
person reported having been diagnosed with a hearing
problem. In addition, none owned a hearing aid. Community
volunteers were paid five dollars for participating.
Materials
The 43 signal words were recorded on audio tape in 18
random orders. Three male and three female speakerswere
used to create the recordings. Each speaker produced a
monotone, emotional, and whisper voiced tape, eachwith the
words in a different random order. In all instancesthe words
were spoken at 8 s intervals (onset to onset). To create the
monotone voice-style recordings, speakerswere instructed to
read the words in a staid, even manner. To create the
emotional recordings, speakers were instructed to say the
words in a way that would tell a loved one about thepresence
of an imminent hazard so that he or she would avoid the
hazard. To create the whisper recording, speakerswere asked
say the words in a “soft” manner. The word sounds were
recordedso that they were roughly similar in amplitude across
the voicing style conditions. The tapes were played back to
participants at either a low (60 dBA) or high (90 dBA) sound
level. All recordings were produced in a sound chamber(to
eliminate background noise) and subsequentlyplayed back to
participants using the following equipment: Audio Technica
ATR30 vocal/instrument microphone, Marantz PMD201
professional portable cassette recorder, and Koss TD/60
enclosed-earheadphones.
Procedure
Initially, each participant was asked to sign a consent
form. The researcher told participants that they would be
hearing a series of words and they were to rate each one on
“How careful would you be after hearing each word?” based
on both the meaning of the word as well as how it sounds.
The ratings were made on a g-point Like&type scale with the
following verbal anchors on the even-points of the scale: (0)
not at all careful, (2) slightly careful, (4) careful, (6) very
careful, and (8) extremely careful. Ratings were marked on a
sheetwith a set of blanks numberedfrom 1 to 43.
Each participant heard three tapes, a monotone, an
emotional, and a whisper voiced tape according a predetlned
setof random orders. A given participant could hear the tapes
presentedat either a low or high sound level spokenby a male
or female. An equal number of male and female participants
were assignedto all conditions.
RESULTS
Two analyseswere preformed on the data. One analyzed
all of the data. The other was restricted to a specific subsetof
five signal words. There were 124 missing ratings out of a
total of 18756 values for the 144 participants (0.66%). In
order to include data for all participants, we replaced the
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Tab/a 1. Intended Carefulness
Voice Style:
speaker Gender:
Mean, SD:
DEADLY
FATAL
LETHAL
EXPLOSIVE
mx1c
POISON
DANGER
DANGEROUS
L%EFUS
CRITICAL
HAZARD
URGENT
HARMFUL
VITAL
CRUCIAL
BEWARE
FORBIDDEN
WARNING
UNSAFE
STOP
HOT
CAUTION
SERIOUS
INJURIOUS
&%?I
EER
ALERT
CAREFUL
PROHIBIT
DON’T
IMPORTANT
K&ENT
ATTENTION
REQUIRED
NECESSARY
NEEDED
NOTICE
NOTE
REMINDER
FACTORS
AND
ERGONOMlCS
SOCIETY
6.62
6.49
:z
5:9a
::ZZ
E
4:90
4.89
4.85
4.84
4.72
4.57
4.55
4.44
tit
4:31
:z
4:1a
tii
4:01
3.93
3.82
3.80
3.76
3.14
3.66
3.54
3.49
3.31
3.28
3.23
iii
2154
253
i:
1.81
1.97
1.91
Male
M
SD
5.78
5.68
2.17
2.14
2.42
1.93
1.81
2.58
1.67
1.91
1.87
1.89
211
E!
~~
2:19
1.85
1.81
1.94
1.88
2.01
1.86
l.%
1.80
2.05
1.95
1.88
2.02
1.87
MEETING-1998
Means for Voice Style, Speaker Gender, and Signal Word.
Emotional
MO?lOtC?E
Overall
M
SD
42nd ANNUAL
:z
5:a5
4.71
4.78
4.65
4.38
4.10
4.38
4.22
4.11
4.15
4.08
4.53
3.96
3.81
3.53
3.72
3.74
3.60
4.17
3.86
1:98
2.03
1.82
2.11
4.13
3.31
3.50
3.57
:z
1:65
2.04
2.05
1.92
2.18
1.92
1.84
2.02
3.75
3.16
3.26
3.03
3.24
3.12
2.50
3.15
3.13
2.69
:z
1:91
2.04
1.88
2.26
2.24
2.22
2.08
1.61
E
1:67
E
1:a5
%
:z
1:97
1.49
1.78
1.98
2.11
1.75
%
1:87
1.59
l.%
1.98
1.87
1.95
1.76
:z
1:67
1.71
1.72
2.26
1.58
Female
M
SD
6.86
7.08
6.82
6.22
6.14
6.28
5.38
5.29
5.65
5.33
5.06
4.99
4.65
5.00
4.99
4.59
4.54
4.77
4.43
4.59
3.91
4.48
4.26
4.18
t:
4:31
3.77
3.82
3.79
3.12
4.10
3.17
3.52
2.90
3.37
3.24
3.21
;z
2:33
2.03
2.11
1.72
1.68
1.76
2.17
2.15
2.08
1.92
1.86
1.90
1.82
2.08
1.94
1.82
1.85
2.01
1.89
1.79
2.01
1.67
1.97
2.20
2.00
1.80
1.95
2.01
1.91
2.03
2.09
1.86
1.92
1.83
2.08
1.92
2.01
2.05
1.94
1.87
1.93
2.01
1.98
1.81
2.04
2.05
M
Male
6.28
6.21
2:
5:72
5.18
5.18
;z
4:63
4.90
4.78
%
4122
4.13
4.21
Et
3:94
4.74
4.10
3.86
4.24
4.23
3.76
3.65
3.52
4.28
3.83
3.78
3.06
4.19
3.33
3.81
3.07
3.18
3.07
2.69
2.78
2.83
2.53
1.71
SD
1.98
2.29
i-E
1:97
2.13
1.81
1.83
1.70
1.86
2.12
1.81
2.11
1.82
%a
1:71
1.86
1.67
E
1:94
1.62
1.71
2.10
:E
io2
1.95
1.82
1.51
2.06
2.05
1.70
2.02
1.83
1.86
2.00
1.79
1.97
212
1.97
1.58
Whisper
Female
M
SD
7.42
z
6:90
6.49
6.67
6.10
5.75
5.92
Z:E
:z
5127
E
5:01
:2
4119
z*t;
4189
4.3 1
4.60
5.18
4.57
4.33
4.17
4.83
i-2
4:17
4.19
4.54
3.90
4.06
3.77
3.38
3.08
3.18
2.58
2.72
1.07
1.85
1.19
1.71
1.86
1.69
1.62
1.61
1.86
1.56
1.82
1.69
1.68
1.55
2.04
:*z
1:78
1.50
1.81
1.96
2.10
:z
1:a7
1.72
1.63
2.21
2.13
2:
1:89
2.06
1.87
2.39
1.99
1.80
2.04
1.91
1.93
1.99
2.10
2.00
Male
M
2.:
6:14
5.85
5.56
:i
5:oa
5.17
4.72
4.75
4.49
3.88
4.36
4.38
4.26
4.59
4.51
3.86
4.50
3.72
3.96
4.01
3.69
3.61
3.79
3.76
E
z;
3:54
3.27
%
22
2:71
2.72
2.21
2.31
1.36
1.93
SD
1.87
1.75
1.79
2.19
1.91
2.06
1.82
1.73
1.94
2.00
1.88
1.81
1.81
E
2:03
2.07
1.93
1.87
1.91
2.04
1.94
1.61
1.95
1.80
:z
2:17
1.91
1.78
1.50
1.86
2.06
1.88
1.89
1.88
1.63
1.92
E
li3
1.50
1.86
Female
M
SD
6.94
6.50
6.63
6.25
6.12
6.14
5.21
5.29
5.25
5.02
5.50
5.17
:2
%3:92
3.19
3.36
3.01
3.19
3.11
2.94
2.81
1:67
2.17
2.21
1.92
2.04
1.80
2.06
1.79
1.97
2.01
2.08
2.00
2.14
2.01
1.97
2.14
1.87
1.91
2.16
2.01
1.80
2.05
2.02
2.12
1.78
2.09
1.98
1.92
1.70
2.09
1.99
2.08
2.14
2.02
1.88
2.21
1.91
%
1:92
2.14
E
2:13
2.02
iii:
4167
4.65
4.33
:z
4:32
4.28
3.94
4.21
3.14
3.69
%
4:n
3.25
measures.
showed a significant main effect for voice style, F(2,256) =
18.51, p c .OOOl. Tukey’s Honestly Significant Difference
(HSD) test showed that the emotional (M = 4.57) voice
produced significantly higher carefulness ratings than the
whisper (M = 4.13) and the monotone (M = 4.09) voices (ps <
.Ol). The latter two conditions were not significantly
different. The ANOVA also showed a significant main effect
for signal words, F(42, 17388) = 262.88, MSe = 2.107, p <
BOO1. The overall meansand standarddeviations are shown
in the left side of Table 1. Comparisons among these main
effect means can be made using the Thkey’s HSD minimum
significant difference of 0.39 (p = .05). None of the other
factors in the full analysis produced significant main effects.
The ANOVA for the full list of signal words showed a
significant main effect for speaker genti F(1,128) = 8.83, p
Words voiced by female speakers (M = 4.53)
< .Ol.
produced significantly higher carefulness ratings than words
voiced by male speakers (M = 4.00). The ANOVA also
The ANOVA also showed severalsignificant interactions.
Only one did not involve signal words - a speakergenderX
voice style interaction, F(2, 256) = 4.90, p < .Ol. These
means are displayed in Table 2. Female speakersproduced
significantly higher carefulnessratings than male speakersfor
missing values with a mean for that particular word within its
respectivecondition.
Full List Analysis
The data set was a six-factor experimental design that
was analyzed using a 2 (Population: students, community
volunteers) X 2 (Sound level: low, high) X 2 (Speaker
gender: male, female) X 2 (Participant gender: male,
female) X 3 (Voice style: monotone, emotional, whisper) X
43 (Signal words) mixed-model analysis of variance
(ANOVA) with the last two factors manipulated as repeated
,
’
PROCEEDINGS
of the HUMAN
FACTORS
AND
ERGONOMlCS
Table 2. Intended Carefulness Means as Function of
Speaker Gender and K&e Style.
Voice Style
Speakergender
Monotone
Emotional
Whisper
Male
3.79
4.19
Female
4.39
4.95
4.01
4.24
mean
4.09
4.57
4.13
mean
4.00
4.52
both the emotional and monotone voice styles (ps < .Ol), but
the speaker-genderdifference for the whisper voice style was
not significant. All of the remaining interactions in the
ANOVA involved signal words. This finding was expected
given that this factor was comprised of 43 levels and any
interaction with signal word would concern conditions that
are multiples of that number. The huge number of conditions
makes it likely that a deviant number in one or more of these
conditions could produce a significant signal word
interaction. The significant interactions involving signal
word are summarized as follows:
In the two-factor
interactions, signal word interacted with (a) population group,
(b) sound level, (c) speakergender,(d) participant gender,and
(e) voice style. In the three-factor interactions, signal word
interacted with (a) speaker gender X population group, (b)
speaker gender X sound level, and (c) population group X
participant gender. There were also two four-factor
interactions involving signal word: (a) population group X
sound level X speaker gender, and (b) population group X
sound level X participant gender. Becauseof the enormous
complexity of these interactions, the associated patterns of
means will not be describedin this report. A complete set of
meansis available from the authors. Table 1 showsthe means
and standarddeviations as a function of the 43 signal words in
combination with two factors that produced significant effects
(individually, together, and with signal word): voice style and
speakergender.
Five Word Analysis
A second analysis of the data was was limited to the five
signal words: DEADLY, DANGER, WARNING, CAUTION
A 2 (Population: students, community
and NOTICE.
volunteers) X 2 (Sound level: low, high) X 2 (Speaker
gender: male, female) X 2 (Participant gender: male, female)
X 3 (Voice style: monotone, emotional, whisper) X 5 (Signal
words) mixed-model ANOVA, with the last two factors
repeatedmeasures,was performed.
The ANOVA showed a significant main effect for
speakergender F(l, 128) = 11.73,p < .OOl. Wordsvoiced by
SOCIETY
42nd ANNUAL
MEETING-1998
1071
female speakers (M = 4.90) produced significantly higher
ratings than words voiced by male speakers(M = 4.30). The
ANOVA also showeda significant main effect for voice style,
F(2,256) = 22.78, pc .OOOl. Tukey’s HSD test showed that
words spoken in the emotional voice (M = 4.99) were rated
significantly higher than those spoken in the monotone (M =
4.34) or whisper (M = 4.47) voice styles @s < .Ol). There
was no difference between the latter two conditions. The
ANOVA showed a significant main effect for the five signal
words, F(4, 512) = 366.02, p < .OOOl. Tukey’s HSD test
showedthat all comparisonsamong the terms were significant
(DEADLY, A4= 6.62; DANGER&f = 5.28; WARNING, M =
4.40, CAUTION, M = 4.18; and NOTICE, M = 2.53) except
betweenWARNING and CAUTION.
The ANOVA also yielded several significant interactions
@s< .Ol). There was a two-factor interaction for population
group X signal word, F(4, 512) = 6.90, p < .OOl. Thesedata
are shown in Table 3. Simple effects analysis showed that
community volunteers rated DEADLY (M = 6.91)
significantly higher than the students (M = 6.33), and students
rated NOTICE (M = 2.81) significantly higher than the
community volunteers (M = 2.24). There were no significant
differences between the population groups for the terms
DANGER, WARNING, and CAUTION. There was also a
significant two-factor interaction for speaker gender and
signal word, F(4, 512) = 3.83, p < .Ol. Table 3 contains the
associatedmeans. Simple effects analysis showed that female
speakers produced significantly higher ratings than male
speakersfor all of the words, except NOTICE.
Table 3. Carefulness Means as Function of Signal
Word, Speaker Gender and Population
Group.
Population Group
DEADLY
Male
Female
DANGER
Male
Female
WARNING
Male
Female
CAUTION
Male
Female
NOTICE
Male
Female
Students
Community
VAunteers
nM?M
5.67
7.00
6.68
7.15
6.18
7.07
4.73
5.68
5.26
5.44
5.00
5.56
3.75
5.01
4.17
4.66
3.96
4.84
3.87
4.56
3.95
4.35
3.91
4.46
2.87
2.75
2.04
2.44
2.46
2.60
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of the HUMAN
FACTORS
AND ERGONOMICS
In addition, there was a significant three-factor interaction for
population X speakergenderx signal word, F(4,512) = 3.39,
p < .Ol. These means are shown in Table 3. Simple effects
analyses were employed to examine the speaker gender X
signal word interaction separately for each population group.
The analysis showed that these two factors significantly
interacted using the student data but not with the community
volunteer data. In general, carefulness ratings were higher
with female speakers than with male speakers for both
population groups except there was no speaker-gender
difference (and a small reversal) for the term NOTICE by the
students.
DISCUSSION
The results generally showed that voice presentation of
signal words produces ratings of intended carefulnessthat are
similar to those found in research assessing the words
presented visually (Wogalter dz Silver, 1990, 1995).
DEADLY is rated higher than DANGER which is in turn
rated higher than WARNING and CAUTION (which did not
differ), and all are higher than NOTICE.
The results also showed that the effects of voiced signal
words are influenced by the way they are presented. Words
voiced emotionally and by female speakers generally raised
carefulnessratings relative to the words voiced in a monotone
or a whisper or by male speakers. The null effect of the
whisper voice fails to support the Mershon and Philbeck
(1991) finding of a difference between whisper and
conversational speech, but we did note that for some signal
words the whisper voice had higher ratings than the emotional
voice (see Table 1). Sound level, participant group, and
participant gender failed to produce main effects, although
these and the other variables entered into various complex
interactions in the ANOVAs.
Research has shown that non-speech auditory signals
presentedat faster rates and at higher frequencies increases
the sounds’ perceived urgency (e.g., Edworthy & Adams,
1996). Words presented by emotional voice might be
characterizedin this sameway: speechexpressedat a higher
rate of speedand at higher frequencies. Note, too, that female
voice are generally higher in frequency than males. In
emergency situations, people generally speak at a faster rate
and at a higher pitch. This effect may be similar to mothers
alerting their children to a potential hazard. Our possible
attunement to these voice characteristics to form urgency
perceptions may have survival value. Furthermore, the
presentresearch suggeststhat these variables (frequency and
rate) are more important for hazard perception than loudness.
The present research is one of the few existing studies
examining factors related to voiced warnings. Clearly more
investigations on this topic are needed given that research
indicates that auditory warnings are capable of substantial
levels of compliance (e.g. Wogalter et al., 1993; Wogalter &
Young, 1991). With the availability of digital voice chips
SOClETY
42nd ANNUAL
MEETING-1998
together with various kinds of detection systems, auditory
warnings can now be practically employed in situations not
previously considered. Of course, auditory warnings can not
be used in every situation. Researchis needed to determine
the kinds of situations where auditory warnings are
appropriate and where they are not.
Although the present researchhad a complex number of
factors and conditions, there are many other parametersof
voice warnings that could influence their effectiveness in
eliciting careful behavior. Such research is needed for
specific warning-design recommendations. optimal
effectiveness of voice warnings may also depend on the
environmental and situational characteristics.
ACKNOWLEDGMENTS
This researchwas funded by a grant to the secondauthor
from the UNC Injury Prevention ResearchCenter. We thank
Carol Runyon and Mike Bowling of the IPRC for their
support. We appreciate Amy Magurno’s assistancein data
collection.
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